TECHNOLOGY
METROLOGY Sensitivity means
The smallest differences in optics and materials require the most sensitive of metrology tools, as Rob Coppinger discovers
W
hen dealing with photons and angstroms your measurement system has got to be good – and whether it is optics, sensors,
laser light or what the light is bouncing off, more accuracy and higher resolutions are what the market is demanding. Beyond the laser there can be few components of any photonics technology more important than the optics, and Armstrong Optical provides systems for measuring optics quality; in particular, their centre thickness. ‘What we’ve designed is a low-cost, non-contact system to get down to five to 10 microns accuracy for measuring the centre thickness of lenses,’ Rob Roach, Armstrong’s sales manager for the optics market told Electro Optics. ‘It would be nice to go to higher precision but then you’re going to £80,000 worth of equipment in a temperature-controlled lab, not an optical workshop. We found people asking for a non- contact gauge for soft optical materials with tens of microns of accuracy.’ Armstrong Optical has received interest from
organisations in Europe for using the system for quality assurance, checking batches of 10 to 20 lenses, and it can be deployed for batch quality-control of hundreds of lenses. Its use as an offline optimisation tool in production is another application for customers.
‘It is material-independent,’ explains Roach. ‘Silicon, silica; it is also form-independent; we can do unpolished rough surfaces, polished surfaces, coated surfaces.’ Roach has several systems in the user community already. ‘We have interest for five or six more systems,’ he adds. Roach finds that selling one system to a customer can encourage them to buy another for production – and sometimes Roach’s customer’s customers also
22 ELECTRO OPTICS l FEBRUARY 2013
competitive advantage
realise that they could benefit from having the same measurement system as their supplier. ‘The customer’s end user can be interested in a system, as having the same tool for measurement ensures consistency from that supplier and others, without increasing the potential to damage components.’ Demonstrating the technology to potential clients, Roach explains that the system was shown to be able to detect a lens’ centre thickness after a high-performance coating had been added. As well as accuracy, another area of improvement is automation. But Roach sees drawbacks with this: ‘One improvement is automation, but if you automate it you end up with a product that is quite expensive. Why would users want it automated, when the automation costs become unjustifiably significant for customers used to making manual thickness measurements?’ he says. For Roach’s customers, high-productivity
throughput is not the goal. These companies are not churning out 10,000 lenses. They are more likely to be producing high-value lenses, and machining such lenses to micron tolerances can mean a number of in-process checks during
production, for consistency. ‘It’s not for high- volume applications, its manual; you put the lens in, you record it, and rework if required. The non-contact technology means no damage to the component during these in-production measurements,’ he adds. Trioptics’ research and development manager is Dr Iris Erichsen. She finds that her company’s markets and customers are asking for automation. ‘More people want completely automated systems and this is something we have seen for a while, which is the same for all of these markets.’ Trioptics’ markets are wide-ranging, from mobile phones to automotive to space. ‘We’ve provided measurement systems to almost anything you want to measure,’ says Erichsen. ‘We are not limited to any one measurement method. We have a wide range of techniques in terms of what we want to measure.’ As well as parameters such as effective focal length and the radius of the curvature of surfaces, Trioptics’ equipment measure the imaging quality of objective lenses, very small, <1mm diameter camera optics for mobile phones and very large lenses. As Erichsen explains, for the
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